[Yaml-core] JSON Compatibility

[Oren Ben-K. <or...@be...>]

Hi people,

Sorry for the long absence - personal reasons. I hope to get more YAML
time from now on.

Brian, Clark and myself discussed the JSON compatibility issue. We
basically see two options:

1. Only require a space after the ":" if the key is plain. So:

   "foo":123 # Becomes valid
   12:34: Meeting # Stays valid
   bar: http://yaml.org # Stays valid

This is backward compatible, and compatible with machine-generated
JSON. It is _not_ compatible with hand written "JSON-like" data like
{foo:bar} - JSON insists on quotes, but hand-written data often lacks
them.

2. Disallow ":" in plain keys.

 "foo":123 # Becomes valid
 12:34: Meeting # Becomes error
 bar: http://yaml.org # Stays valid

This is not backward compatible, as keys with ":" in them will break.
To minimize this, we can specify that the above rule only holds in
flow context (inside {}). Presumably all YAML that contains : in keys
has it in block context (outside {}). So {12:34: meeting} will be an
error but the above example will stay valid.

Personally, I feel that (1) is a better way, as it is fully backward
compatible and fully JSON compatible. AFAIK the vast majority of JSON
is written by machines and not by people, and the JSON spec is clear
that " are mandatory so all libraries emit them. I also think that
having such a subtle difference between block and flow keys would be
too confusing. Finally, option (1) is such a minor relaxation of the
spec that I doubt its worth to bump YAML's version number for it.
Option (2) is definitely a YAML 1.2 thing, which I feel is an
overkill.

Brian has been... persuaded... to accept option (1) <grin>, which
leaves Clark to get a concensus. Clark?

Have fun,

   Oren Ben-Kiki